DNA left on objects can be traced to people, study says

NEW YORK - Think you're a tidy person? A new study suggests you're leaving DNA all over the place - on pens, keys, coffee mugs - and it can be traced back to you.

That provides a handy tool for investigating crimes, say forensic scientists who recovered DNA from a slew of everyday things and matched it back to the people it came from.

The technique has already been used to provide evidence in cases of attempted murder, rape, armed robbery, extortion and drug trafficking, the Australian scientists said.

At the same time, the researchers found that people can pick up other people's DNA on their hands. That raises at least the possibility that a person could plant or accidentally leave somebody else's DNA at a crime scene.

Most people know DNA can be recovered from blood or semen, and they may have heard that evidence in the Unabomber case includes DNA recovered from some licked stamps.

Scientists said it's no surprise that DNA can also be found on objects that were only casually touched by hands. Prior reports have described getting it from doorknobs, for example.

Still, the Australian work is striking in suggesting that so much DNA can be recovered so consistently from so many things, experts said.

"It's more common than we would have expected. It seems less a chance occurrence," said Ron Fourney of the Royal Canadian Mounted Police.

The new work is presented in today's issue of the journal Nature by Roland A.H. van Oorschot and Maxwell K. Jones at the Victoria Forensic Science Center in Victoria, Australia.

It's not clear where the DNA that people shed casually comes from, Mr. van Oorschot said. But there is some evidence that "naked" DNA - DNA that has escaped from dying cells - can be on the skin, he said.

The researchers recovered DNA from leather briefcase handles, pens, a car key, a locker handle and telephones, and found the samples matched the DNA of people who regularly used each item. One of the phones also yielded the genetic profile of somebody who used it only occasionally.

They also found that people left identifiable DNA on plastic knife handles, a mug and a glass after handling them for only 15 minutes. New vinyl gloves, worn for 20 to 90 minutes, gave the genetic profile of whoever wore them.

DNA could be picked up even from plastic tubes that had been held for only five seconds. When two or three people handled tubes, DNA from the different users could be recovered.

DNA left by one person on a tube was often found on the hands of people who handled it later, and the researchers found that DNA from one person could pass to another during a one-minute-long handshake.

If a person can pick up your DNA from a handshake or something you touched, does that mean that person could then leave your DNA on something at a crime scene, falsely suggesting you were there?

It's not clear, and it will take further experiments to find out, Mr. Fourney said. But the amount transferred in this secondhand way would be so tiny it probably would not be detected, Mr. Fourney said.

And if it were detected, the tiny trace would probably not have much effect on interpreting the overall DNA evidence from the scene, he said.

If people are leaving DNA in so many places, does that mean anybody else could secretly obtain it and find out somebody's genetic profile?

Yes, but that's nothing new, said George Sensabaugh, a professor of forensic and biomedical science at the School of Public Health at the University of California at Berkeley.

"People have been able to get that in other ways that you may not appreciate either," he said. "People could pluck your hairs. You may not be aware your hair is being plucked if you're jostled" on the subway.

And DNA can be retrieved from somebody's toothbrush or hairbrush, he noted.